Method for preparing a physical plaster model

ABSTRACT

The invention provides a method for creating a physical teeth model. The method comprises the following steps: providing a virtual three dimensional (3D) representation of a patient&#39;s dentition that comprises at least a region of the teeth that includes a tooth stump on which a crown is to be fitted or a region on to which a bridge is to be fitted; and preparing a physical model of the jaws of a subject from a blank, based on information from said virtual 3D image.

CROSS-REFERENCE TO EARLIER FILED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.10/676,257 filed on Oct. 2, 2003 now U.S. Pat. No. 7,220,124 and claimsbenefit of U.S. Provisional Patent Applications 60/415,931 filed Oct. 3,2002 and 60/422,782 filed Oct. 31, 2002, the entire contents of whichare hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to the field of dentistry and in particular to amethod of preparing plaster models for use in orthodontics,prosthodontics and other aspects of dental medicine.

BACKGROUND OF THE INVENTION

For a dentist or a dental technician, one of the main difficulties inmaking a working physical model of the teeth, including theinter-occlusal relationship between the jaws (also known by the term“master cast” or “working cast”), lies in respecting the position of apatient's artificial jaws when the teeth are in Centric Occlusionposition. Separate molding of the upper and the lower teeth followed bythe manual articulation of the two parts is a constant source of error.The precision of the cast depends on several factors, including, interalia, the accuracy of the impressions and wax bites, the material fromwhich the cast is constructed, and the identification of the anatomic.In addition, traditional methods using pins do not prevent linearexpansion of the cast. This can result in the deformation of the newteeth that do not correspond perfectly to the original. Thus, the moreprecisely the working cast reproduces the anatomy of the mouth, the moreaccurate will be the spatial position, and the static and dynamicrelationships. This provides a better possibility of producing abiomechanically acceptable restoration.

In order to reproduce with high precision the mechanical equivalent offunctional and non-functional movements within the mouth, articulators(also known by the term “occluding devices”) have been and still areunder development. The articulators are used to precisely hold models ofa patient's upper and lower teeth, so a dentist can study their bite ormake a restoration.

Articulators are primarily used when a crown needs to be prepared.According to current practice, after diagnosing in a patient the needfor a crown or a bridge, the dentist cuts the tooth to be reconstructedby the crown or bridge and prepares two impressions and a wax bite ofthe patient's jaws. One impression is of the area prepared for the crownand the surrounding area. The other impression is of the opposite jaw. Awax bite is used to record the spatial relation between the jaws atocclusion. Based on the impressions, wax bite and written instructionsof the dentist, a technician prepares in a lab the corresponding plasterjaws which are trimmed and mounted on an articulator. Using the waxbites, the spatial relation between the jaws is determined. At thisstage, the tooth within the preparation to be reconstructed istemporarily separated from the plaster so that the area with theanatomic information (the area defining the anatomic contour) and thefinish line are exposed. The finish line is typically marked manually bythe lab technician in ink on the preparation and a crown is built basedon the resulting preparation. The quality of the crown prepared isexamined by placing the crown on the preparation in the articulator andverifying that there is a good occlusion of the crown with the oppositeteeth. If in the affirmative, the crown is sent to the dentist forplacement on the preparation in the patient's mouth.

SUMMARY OF THE INVENTION

The present invention concerns a unique method of preparing a physicalworking teeth model of teeth, e.g. a model made of hard plaster, usedfor the fabrication of orthodontics and prosthodontics Crown or Bridges.The method utilizes a three dimensional (3D) virtual image of thepatient's dentition or parts of it. Based on digital data representingsaid 3D image, a physical 3D teeth model is constructed.

The term “teeth model” will be used to denote a physical,three-dimensional representation of teeth in a solid matrix having asurface relief corresponding to the teeth arrangement of the individual.Such a model may be a “positive teeth model”, comprising a teethreplica, namely, a model where each tooth is represented by a projectionor bulge having contours identical in size and shape to thecorresponding tooth; or a “negative teeth model”, where each tooth isrepresented by a cavity or recess with contours identical in size, butopposite in shape to the contours of the corresponding tooth.

Thus, according to one embodiment, the invention provides a method forpreparing a physical positive working model of a patient's dentition.According to another embodiment, the invention provides a method forpreparing a physical negative model from which a positive working modelcan be fabricated, according to known dentistry procedures.

The method of the invention is of particular use in the construction ofcrowns or bridges. Thus, according to the invention, the 3D virtualimage comprises at least the region of the teeth that includes a toothstump on which a crown is to be fitted or a region on to which a bridgeis to be fitted. Based on the virtual image of the dentition, a physicalmodel of the two jaws is prepared. Thereafter, the resulting model,being positive or negative, as the case may be, is used for a variety ofpurposes, for example to prepare a crown, a bridge or other dentalappliance; to analyze the relationship between the upper and lower jaws;to show the patient the crown or bridge; etc.

Alternatively, the virtual image may be further manipulated and based onthe digital data representing the image, a virtual crown or bridge isconstructed. Based on the virtual image of the crown or bridge, aphysical model of the crown or bridge is prepared.

A virtual three-dimensional (3D) image is obtained e.g. in the manner asdescribed in PCT publication No. WO97/03622 or PCT publication No.WO00/08415.

The dentist (or the technician, as the case may be) may construct avirtual image of the patient's dentition either with or without thevirtual image of the crown or bridge, and then may send such data to thelab technician. There, a physical model may be prepared, e.g. bymilling, 3D lithography or by any other appropriate means, according tosaid data. The physical model prepared by the technician can be sent tothe dentist, for his approval (the physical model can also be fabricatedat the dentist's office).

The physical model has typically one member that represents the upperjaw and another that represents the lower jaw. It order to render iteasy to match these two members to one another, they may be producedwith markings or appropriate physical alignment arrangement for aligningthe jaws to represent the alignment of the jaws of the patient. Saiddata that includes the virtual image thus preferably includes also databits for producing such markings or arrangement.

Markings may be in the form of depressions or protrusions on the face ofthe members that are made such so as to provide the technician with atool for the proper alignment of the two members. A physical alignmentarrangement may include a mounting arrangement for mounting the twomembers to an articulator to yield a proper occlusion alignment. Byanother example, the physical alignment arrangement may include one ormore alignment reference components in one member that once fitted withone or more corresponding components in the other member, ensure properalignment of the two members.

Thus, the present invention provides a dental articulator that preciselysimulates the occlusion relationship of the jaws as well as thethree-dimensional movement of a human jaw.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, a preferred embodiment will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings,in which:

FIG. 1 shows, by way of a block diagram, a computerized device forconstructing a virtual impression of the patient's dentition.

FIG. 2 shows, by way of a block diagram, a computerized device formilling a plaster model, based on the information from the virtualimpression, in accordance with an embodiment of the invention.

FIG. 3 shows a perspective view of the plaster model arranged on anarticulator.

FIG. 4 shows a perspective view of the plaster model with references foraligning the jaws;

FIG. 5 shows, by way of a flow chart, a method for fabricating aphysical teeth model, in accordance with an embodiment of the invention;

FIG. 6 and FIG. 7 illustrate two specific examples, respectively, of themethod of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

As is true in any method of making a physical model, e.g. a plastermodel of a patient's dentition, it is most important to start with anaccurate representation of the jaws and teeth and the inter-occlusalrelationship between the jaws. For this purpose, the instant inventionrelies on a virtual model of the patient's dentition.

Digital data representing a virtual teeth model may be obtained by avariety of methods, such as that described in PCT Application No.PCT/IL96/00036 (publication No. WO97/03622) and in PCT Application No.PCT/IL99/00431 (publication No. WO00/08415). The virtualthree-dimensional image may be manipulated, for example, in a mannerdescribed in PCT Application No. PCT/IL99/00577 (publication No.WO00/25677). In particular, the virtual three-dimensional (3D) image isobtained by utilizing a physical negative teeth model, e.g. a negativeteeth model that comprises the teeth impression by means of animpression matrix. The physical negative teeth model may be used assuch, thus providing digital negative representation of the patient'sdentition, from which a digital positive representation of the patient'sdentition may be digitally obtained. Alternatively, the physicalnegative teeth model may be used to prepare a physical positive teethmodel, from which a digital positive teeth representation is provided.

After the virtual image is generated, the display is typically acomputerized display, provided with software permitting the technicianto visualize the virtual image from different angles. As will beappreciated, the invention is not limited to any specific display meansand any means for presenting the image such as, for example, in aprinted format, on a computer display screen, etc., may be employed inaccordance with the invention.

In most situations, the dentist will take three virtual impressions. Oneimpression is of the preparation area for the crown, bridge or otherdental appliances, along with the surrounding teeth. Another impressionis of the teeth on the opposite jaw. The third impression records thespatial relationship between and the spacing of the two jaws in acentric occlusion. This information from the virtual impressions isplaced in a 3D file that contains the two jaws and the spatialrelationship between them in occlusion. Thereafter, the 3D file may betransferred to the laboratory.

Reference is made to FIG. 1 showing a computerized device generallydesignated 20 including a processor 22 and a display unit 24. Running inthe processor 22 is a first software utility 26 that receives an inputof a three dimensional virtual teeth model and then processes,automatically or through the user, manipulable software utility 28, toconstruct a three dimensional virtual teeth model that includes theregion that is to be treated, which can then be fed for display todisplay unit 24. By this means, the virtual impression of the dentitionis made and the information may then be stored. The technician may thensimulate any treatment area on the computer. For example, the cutout inthe tooth for the crown can be simulated, along with fitting of thecrown.

Reference is now being made to FIG. 2 showing a system generallydesignated 40. In FIG. 2, like components to those shown in FIG. 1, aregiven the same reference numerals shifted by 20 (namely component 42,for example, is functionally identical to component 22 in FIG. 1).System 40 of FIG. 2 includes an apparatus 50 that is used to construct aphysical model utilizing digital data received from software utility 48.For this purpose, a Computer Numerical Control (CNC) milling machine 50may be used. However, the invention is not limited to the use of a CNCmachine and any other CAM (Computer Aided Manufacturing) technology thatcan produce a physical model out of virtual data may be used.

To manufacture a crown, a bridge, or any dental appliance, the labtechnician requires two physical jaws models mounted on an articulatoror placed in the correct spatial orientation one against the other.According to this method, the information for the two jaws and theirspatial relationship in occlusion is in a digital 3D file.Alternatively, or in addition, the proper occlusion may be determined ina manner disclosed in WO 98/52493. The computer guided milling (or othertechnology) machine is connected to the computer with the 3D file of thevirtual impression, and then a physical model of each one of the jaws ismilled from a blank made of plaster, or other appropriate materialtaking into consideration also the spatial relation between the two jawsand their occlusion. At this point, the technician has his necessaryphysical model and can proceed with making the crown or the bridge.

Based on information from the virtual 3D image, the dentist or atechnician may generate a 3D model of a crown to be fitted on a toothstump or of a bridge to be fitted on the tooth surface, to generate adigital file on which basis the lab technician, through the use of acomputer driven milling machine, may generate a physical crown, bridgeor other dental appliances.

It should be noted that the physical model generated by device 40 mightbe a positive model or alternatively, a negative model. FIG. 3 showsplaster cast members 100 and 102 fabricated according to the inventionand representing the upper and lower jaws, respectively. The members 100and 102 can be mounted on an articulator 104 to simulate the properocclusion relation. For that both members have articulator engagementportions 106 with reference holes 108 that can be registered with holes110 engagement bit 112 of articulator 104, which engagement is throughpins 114. The engagement portion 106 with the reference holes 108, areinitially defined in the virtual 3D image. In this model the properinter-jaw occlusion are first defined, as explained above, and after theproper inter-jaw occlusion is determined, the virtual 3D model may bevirtually combined with an articulator to define thearticulator-engagement portion with its reference holes. This is thenincluded in the digital file used to produce the plaster model. Thereference holes may be produced automatically by the milling machine.However, the reference holes may be difficult to produce by the millingmachine and may need to be produced after milling, as a separate step,for example, based on markings produced automatically during the millingprocedure.

Reference is now made to FIG. 4 that shows another embodiment of amanner for proper alignment of the two cast members. The two castmembers 120 and 122 are produced each with a corresponding aligningstructures 124 and 126. Each of these aligning structures includespositioning reference components 124R and 126R, respectively, the formerhaving an end abutment, that fits into a matching recess in the latter.This alignment structure is first produced virtually after virtualalignment of the two jaw members and thereafter structures 124 and 126may then be added. The data file prepared from the virtual model andthat is utilized for manufacture of the physical members 120 and 122,this includes, according to this embodiment, also data for integralproduction of said structures.

As may be appreciated, the lab technician has to build a crown, abridge, or other dental appliances, that will have a good fit on theprepared area of the tooth. Contact with the surrounding teeth must begood, and such as in the case of crowns, there must also be correctcontact with teeth on the opposing jaw. If the crown does not fitcorrectly, the bite will be affected and the crown will not fitcomfortably in the mouth. The articulator is used to mount the model, sothe crown and be formed and properly fitted. This is why the model mustbe highly accurate, or the crown will not fit correctly in the patient'smouth. It is from this information that an accurate 3D file of thedentition is created, and the milling of the plaster physical mold isbased on the information in this 3D file. Due to the enhanced accuracyof the information about the dentition, the physical model can be mademore more accurately, thereby leading to a more accurate manufacture ofthe crown.

Reference is now being made to FIG. 5, and the reader is referred toFIG. 2 for a complete understanding of their function. Illustrated inFIG. 5 are the main steps 100 in a method of the invention for thefabrication of a physical teeth model utilizing the device 40 and a CAMmachine (CNC milling machine 50, in this example) connectable to thedevice 40, as shown in FIG. 2.

At step 125, the device 40 receives an input of a 3D virtual teeth model(constituting a 3D representation of a patient's dentition), and basedon which, generates, at 140, digital information for the fabrication ofa physical teeth model. Then at step 160, the machine 50 fabricates thephysical teeth model.

It should be noted that additional steps might be needed and carried outmanually or automatically, e.g., for the generation of additionaldigital information, which can be displayed by the display utility 24,as previously explained. It should also be noted that the machine 50does not need to be part of the device 40 and can be a separate utility.In the later case, the digital information generated by the device 40 istransmitted to the machine 50 via a direct connection (through wires orwireless communication means) or via a communication network (e.g. theInternet).

According to the common CAD techniques, soft materials such as wax maybe used for the fabrication of the physical model. However, thefabricated physical model made of such relative soft materials is easilydeformable by mechanical stresses. This outcome is highly undesirable inthe context of dentistry, in which a positive working model is used, forexample for the creation of orthodontic or prosthodontics appliances.Any deformation in the fabricated positive model degrades the precisionof the appliance based on the positive model, as well as degrades thequality of the orthodontics and prosthodontics treatment.

The present invention, by one of its embodiment, solves the aboveproblem by providing a method for the fabrication of a precise negativemodel, from which a positive working model can then be produced, forexample from a hard plaster, by utilizing traditional dentistryprocedures.

FIG. 6 and FIG. 7 more specifically illustrate flow diagrams 200 and 300(respectively) for the fabrication of a negative teeth model utilizingthe method of FIG. 5. In the example of FIG. 6, the device 40 receivesan input of a 3D virtual positive teeth model (step 220), and generatesdigital information for the fabrication of a physical negative teethmodel (step 240). The machine 50, being a part of or connectable to thedevice 40, operates to fabricate the physical negative teeth model (step260). At a later stage (not shown), the fabricated physical negativeteeth model is used for the fabrication of a positive working model,according to known procedures, e.g. by filling the negative cast with ahard plaster and removing the negative cast.

In the example of FIG. 7, the device 40 receives an input of a 3Dvirtual negative teeth model (step 320). The processing of this data forthe generation of the digital information for the fabrication of thephysical negative teeth model (at step 340) might not need thegeneration of a digital positive model. However, an additional step (notshown) can be carried out between steps 320 and 340, in which a digitalpositive model, from which the information is derived, is generated.

As mentioned above, the fabricated physical model can bear marking orarticulator engagement portions, for proper relations. When a negativemodel is fabricated, it bears a negative marking and/or engagementportions (e.g. depressions), thus providing the positive working modelwith positive marking and/or engagement portions (e.g. correspondingprotrusions).

It should be noted that a dedicated device could implement theprocedures 100, 200 and 300. Alternatively, these procedures can beintegrated with other computerized dentistry methods, e.g. virtualtreatment plan and the like.

While some preferred embodiments have been shown and illustrated, it isto be understood by a skilled person that it is not intended thereby tolimit the disclosure, but rather it is intended to cover allmodifications and arrangements falling within the spirit and scope ofthe present invention.

1. A system for use in fabricating a dental crown or dental bridgecomprising: an articulator having a plurality of engagement pins and aphysical teeth model comprising two members, a first member representingat least a part of an upper jaw and a second member representing atleast a corresponding part of a lower jaw of a patient, said physicalteeth model being made from a model material and further comprising: analignment arrangement for permitting proper occlusion alignment of thetwo members of the physical teeth model, said proper occlusion alignmentcorresponding to a virtual three-dimensional data file representation ofsaid patient's jaws and from the spatial relationship between saidpatient's jaws in occlusion, said alignment arrangement comprising aplurality of reference holes provided in said members for receiving indirect contact engagement pins of an articulator for providingengagement of the physical teeth model to the articulator via said pins.2. The physical teeth model according to claim 1, wherein said physicalteeth model is a plaster model and wherein said physical teeth model isa positive teeth model.
 3. The physical teeth model according to claim2, wherein the alignment arrangement includes a mounting arrangement formounting said two members on an articulator.
 4. The physical teethmodeling model according to claim 1, wherein said reference holes aremachined into said model material of said two members.
 5. A system foruse in fabricating a dental crown or dental bridge comprising: anarticulator having a plurality of engagement pins and a physical teethmodel comprising: two members, comprising model material, the firstmember representing at least a part of an upper jaw and a second memberrepresenting at least a corresponding part of a lower jaw of a patient,said physical teeth model further comprising: an alignment arrangementintegrally formed with said two members to permit proper occlusionalignment of the jaws of said physical teeth model, said properocclusion alignment corresponding to a virtual three-dimensional datafile representation of said patient's jaws and from the spatialrelationship between said patient's jaws in occlusion, wherein thealignment arrangement includes one or more alignment referencecomponents included in a respective alignment structure in each of saidtwo members, said alignment reference components in the two memberscorresponding to one another with each alignment reference component inone of said two members configured for fitting with the correspondingalignment reference component in the other of said two members and foryielding proper occlusion alignment of the two members.
 6. The physicalteeth model according to claim 5, wherein said physical teeth model is aplaster model.
 7. The physical teeth model according to claim 5, whereinsaid physical teeth model is a positive teeth model.